1. Field of the Invention
The present invention relates to a data processing method whereby data are transmitted between a plurality of acquisition means with a plurality of channels and a central receiver and recording device, using a plurality of transmission modules, each of which is essentially allocated a corresponding data acquisition means.
The present invention is principally intended for use in connection with marine seismic surveys. However, it is to be understood that the method may be applied to seismic data processing in general; e.g., also for processing of data collected in connection with onshore seismic surveys.
For simplicity's sake, however, the present invention is to be described by the example of its application in a marine, seismic system.
2. Description of the Prior Art
In marine seismic surveys there is used a seismic vessel which is steered along specific survey lines of the area to be explored for possible hydrocarbon deposits or the like, while a so-called seismic streamer cable which may have a length of several kilometers, is towed through the sea behind the vessel. Behind the vessel there are also towed means for generating sound waves which are transmitted towards the seabed. The sound waves are reflected from the seabed and strata beneath it and are received by sensitive hydrophones arranged along the seismic streamer.
A group of hydrophones (or geophones) forms part of a so-called seismic data acquisition means; and the analogue measurements from the several sensors are transmitted through measuring channels and digitized in modules which are located adjacent to the acquisition means. The digital data are then transmitted by a digital transmission system to the central receiver and recording means.
As a response to the desire of having a denser spatial sampling within the field of marine seismics, an increasing number of channels are now used for transmitting the reflection signals returned to the streamer by the several sensors which are connected to just as many measuring channels. The number of channels used are rapidly increasing in order to improve the resolution and the information content of the total survey.
The reflection signals in the form of digital signals which are fed to large computers for processing on board the seismic vessel, represent a great volume of information. In connection with the use of an increasing number of channels it has thus been shown necessary to apply a "data reduction" method in order to avoid overflowing the processing centers with data.
It is, however, important when using data reduction that there is a fixed geometry as regards the channels, i.e. a uniform distance between each channel.
In certain cases it is practically impossible physically to maintain a fixed geometry, i.e. because there are used certain defined types of equipment in the streamer, e.g. large compasses, which demand a great deal of space.